1. Field of the Invention
This invention relates to digital communication systems, and more particularly to serial data communication systems employing time division multiplexing to combine several different serial data channels into single serial data streams.
2. Description of the Relevant Art
A transmission medium carries signal-encoded information (i.e., data) from one point to another. Common types of transmission media include metal wires for carrying electrical signals, fiber-optic cables for conveying light signals, and air through which electromagnetic signals (e.g., light and radio waves) travel. As digital signals are more immune to degradations suffered along transmission media, data is often transmitted over transmission media in digital form. For example, telephone service providers typically digitize analog speech signals before conveying the speech signals over relatively long lengths of transmission media. Each telephone conversation may be represented by a serial stream of binary digits (i.e., bits) having a beginning and an end, generally constituting a data “channel.”
A given transmission medium may be able to handle the transmission of several different data channels at the same time (e.g., several different telephone conversations occurring simultaneously). In this case, each data channel may be assigned a periodically recurring block of time (i.e., a “time slot”) for transmission of digital data upon the transmission medium. A transmitting digital communication system may combine the digital data of several individual data channels into a single serial data stream using TDM, then transmit the serial data stream upon the transmission medium. A receiving digital communication system may receive the serial data stream via the transmission medium and separate the data of the individual data channels, thus reforming the individual data channels.
In order to allow the detection of possible errors occurring during transmission of the channel data via the transmission medium, the data of each individual data channel is typically divided into discrete units called “frames.” Error control information is derived from the framed data, and is transmitted along with the framed data. The error control information allows for the detection and/or correction of transmission errors. A transmitting digital communication system encapsulates channel data into frames, generates the error control information associated with the frames, incorporates the error control information into the frames, and transmits the frames upon the transmission medium. A receiving digital communication system receives the framed data from the transmission medium, extracts the error control information from the frames, checks the framed data for errors, and reassembles the channel data from the framed data. All of the above actions are performed according to a selected communication protocol.
There are numerous protocols currently being used for conveying serial data streams upon a transmission medium, including T1, E1, and the high-level data link control (HDLC) protocol. Each serial data communication protocol achieves data transmission in a different way, and digital communication system hardware and/or software designed to implement one serial data communication protocol will typically not recognize data transmitted using another serial data communication protocol. In addition, new serial data communication protocols are continuously being developed in an effort to increase the rates and reliabilities of digital data transfers.
A microcontroller is an integrated circuit which incorporates a processor core along with one or more support circuits on the same monolithic semiconductor substrate (i.e., chip). The support circuits perform support functions such as communication functions and memory interface functions. Systems which employ microcontrollers are typically implemented using fewer separate semiconductor devices. Advantages of such systems include shortened design times, lower fabrication costs, and higher reliabilities. Microcontrollers find applications in industrial and commercial products including control systems, computer terminals, hand-held communications devices (e.g., cellular telephones), network interface equipment, photocopier machines, facsimile machines, and hard disk drives.
It would be beneficial to have a digital communication system capable of transmitting and receiving serial data using time division multiplexing and organized in a functional manner such that the digital communication system may be easily configurable and/or modifiable to convey the serial data via any serial data protocol.